If you need to abort a running Job then the best approach is to 'Kill' the Flow in Azkaban, which in turn will update the job status in RED thus keeping the two systems in sync. 

Navigate to the running Flow Execution and click the 'Kill' button to stop the current execution and synchronize  the job status in RED.

Aborting a job from the RED UI is possible from RED 10.5+ but this action does not synchronize the related Azkaban execution so should really only be used when your Azkaban execution has finished but RED UI is showing it as still running. 

A job can be aborted by right-clicking the job in the RED Scheduler window and choosing Abort Job from the context menu.

Once in this state, a job cannot be restarted. The job now only exists as a log of what occurred and is no longer regarded as a job.